Doubly Linked List


A doubly linked list is a type of linked list in which each node contains a data element and two pointers, one pointing to the next node in the sequence (like a regular linked list) and another pointing to the previous node. This bidirectional linking enables easy traversal in both directions.

Here's a breakdown of the doubly linked list and various operations:

Doubly Linked List Structure:

A node in a doubly linked list typically looks like this in a C-style struct:

Doubly Linked List Node Structure

struct Node 
{ int data; 
struct Node* next; 
struct Node* prev; 
};
data: Holds the actual data of the node.
next: Points to the next node in the list.
prev: Points to the previous node in the list.



Doubly Linked List Operations:

Insertion:

At the beginning (prepend):
Create a new node.
Set its next to the current head.
Set the prev of the current head to the new node.
Update the head to the new node.


struct Node* insertAtBeginning(struct Node* head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;
    newNode->next = head;
    newNode->prev = NULL;

    if (head != NULL) {
        head->prev = newNode;
    }

    return newNode;
}

At the end (append):
Create a new node.
Set its prev to the current tail.
Set the next of the current tail to the new node.
Update the tail to the new node.

struct Node* insertAtEnd(struct Node* head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    struct Node* last = head;

    newNode->data = data;
    newNode->next = NULL;

    if (head == NULL) {
        newNode->prev = NULL;
        return newNode;
    }

    while (last->next != NULL) {
        last = last->next;
    }

    last->next = newNode;
    newNode->prev = last;

    return head;
}


In the middle (insert after a specific node):
Create a new node.
Set its next to the next node of the specified node.
Set its prev to the specified node.
Update the next of the specified node to the new node.
Update the prev of the next node to the new node.


struct Node* insertAfter(struct Node* head, struct Node* prevNode, int data) {
    if (prevNode == NULL) {
        printf("Previous node cannot be NULL");
        return head;
    }

    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;
    newNode->next = prevNode->next;
    newNode->prev = prevNode;
    prevNode->next = newNode;

    if (newNode->next != NULL) {
        newNode->next->prev = newNode;
    }

    return head;
}


Deletion:
Image credit:geeksforgeeks

At the beginning:
Update the next of the head to the next node.
Update the prev of the new head to NULL.
Free the memory of the old head.

struct Node* deleteAtBeginning(struct Node* head) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return NULL;
    }

    struct Node* temp = head;
    head = temp->next;

    if (head != NULL) {
        head->prev = NULL;
    }

    free(temp);
    return head;
}



At the end:
Update the prev of the tail to the previous node.
Update the next of the new tail to NULL.
Free the memory of the old tail.

struct Node* deleteAtEnd(struct Node* head) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return NULL;
    }

    struct Node* temp = head;
    while (temp->next != NULL) {
        temp = temp->next;
    }

    if (temp->prev != NULL) {
        temp->prev->next = NULL;
    } else {
        head = NULL;
    }

    free(temp);
    return head;
}


In the middle (delete a specific node):
Update the next of the previous node to the next node of the specified node.
Update the prev of the next node to the previous node of the specified node.
Free the memory of the specified node.

struct Node* deleteNode(struct Node* head, struct Node* delNode) {
    if (head == NULL || delNode == NULL) {
        printf("List is empty or node to be deleted is NULL.\n");
        return head;
    }

    if (delNode->prev != NULL) {
        delNode->prev->next = delNode->next;
    } else {
        head = delNode->next;
    }

    if (delNode->next != NULL) {
        delNode->next->prev = delNode->prev;
    }

    free(delNode);
    return head;
}



Traversal(Display):
Traverse the list from the head to the tail or vice versa using the next and prev pointers.

void traverse(struct Node* head) {
    struct Node* temp = head;
    while (temp != NULL) {
        printf("%d<--> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}

Search:
Traverse the list and compare the data of each node with the target value until the node is found or the end of the list is reached.

Advantages of Doubly Linked List:
    Bidirectional Traversal: Easy traversal in both directions.
    Insertion and Deletion: Efficient insertion and deletion operations at both ends and in the middle.
    We can quickly insert a new node before a given node.
    In a singly linked list, to delete a node, a pointer to the previous node is needed. To get this previous     node, sometimes the list is traversed. In DLL, we can get the previous node using the previous        
    pointer  
Disadvantages:
    Extra Memory: Requires extra memory for the prev pointers.
    All operations require an extra pointer previous to be maintained. For example, in insertion, we need      to modify previous pointers together with the next pointers.
Complexity: 
    Slightly more complex implementation compared to singly linked lists.
    Algorithms Complexity:
    Insertion/Deletion at the beginning or end: O(1)
    Insertion/Deletion in the middle: O(n) (where n is the number of nodes)
    Search: O(n)

These complexities are based on the assumption that you have a reference to the node where you want to perform insertion, deletion, or search. If you need to search for a node first, additional time will be required.


Doubly Linked List- C program Implementation
/************************************************************************/
#include <stdio.h>
#include <stdlib.h>

struct Node {
    int data;
    struct Node* next;
    struct Node* prev;
};



struct Node* insertAtBeginning(struct Node* head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;
    newNode->next = head;
    newNode->prev = NULL;

    if (head != NULL) {
        head->prev = newNode;
    }

    return newNode;
}

struct Node* insertAtEnd(struct Node* head, int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    struct Node* last = head;

    newNode->data = data;
    newNode->next = NULL;

    if (head == NULL) {
        newNode->prev = NULL;
        return newNode;
    }

    while (last->next != NULL) {
        last = last->next;
    }

    last->next = newNode;
    newNode->prev = last;

    return head;
}

struct Node* insertAfter(struct Node* head, struct Node* prevNode, int data) {
    if (prevNode == NULL) {
        printf("Previous node cannot be NULL");
        return head;
    }

    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    newNode->data = data;
    newNode->next = prevNode->next;
    newNode->prev = prevNode;
    prevNode->next = newNode;

    if (newNode->next != NULL) {
        newNode->next->prev = newNode;
    }

    return head;
}

struct Node* deleteAtBeginning(struct Node* head) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return NULL;
    }

    struct Node* temp = head;
    head = temp->next;

    if (head != NULL) {
        head->prev = NULL;
    }

    free(temp);
    return head;
}

struct Node* deleteAtEnd(struct Node* head) {
    if (head == NULL) {
        printf("List is empty. Nothing to delete.\n");
        return NULL;
    }

    struct Node* temp = head;
    while (temp->next != NULL) {
        temp = temp->next;
    }

    if (temp->prev != NULL) {
        temp->prev->next = NULL;
    } else {
        head = NULL;
    }

    free(temp);
    return head;
}

struct Node* deleteNode(struct Node* head, struct Node* delNode) {
    if (head == NULL || delNode == NULL) {
        printf("List is empty or node to be deleted is NULL.\n");
        return head;
    }

    if (delNode->prev != NULL) {
        delNode->prev->next = delNode->next;
    } else {
        head = delNode->next;
    }

    if (delNode->next != NULL) {
        delNode->next->prev = delNode->prev;
    }

    free(delNode);
    return head;
}

void traverse(struct Node* head) {
    struct Node* temp = head;
    while (temp != NULL) {
        printf("%d<--->", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}

int main() {
    struct Node* head = NULL;

    head = insertAtEnd(head, 10);
    head = insertAtBeginning(head, 5);
    head = insertAfter(head, head->next, 7);
    head = insertAfter(head, head->next, 100);
    head = insertAfter(head, head, 200);
    printf("Doubly Linked List: ");
    traverse(head);

    head = deleteNode(head, head->next); // Delete the node with data 5

    printf("Doubly Linked List after deletion: ");
    traverse(head);

    head = deleteAtBeginning(head);
    printf("Doubly Linked List after deletion at the beginning: ");
    traverse(head);

    head = deleteAtEnd(head);
    printf("Doubly Linked List after deletion at the end: ");
    traverse(head);

    return 0;
}




Comments

Post a Comment

Popular posts from this blog

Data Structures CST 201 KTU Third Semester Syllabus Notes and Solved Questions- Dr Binu V P 984739060

Dr BinuV P -About Me About The Course Syllabus Data Structures Lab CSL 201 ( Do the Programs to Understand the Concept Well) Model Question Paper CST 201 Data Structures University Question Papers CST 201 Data Structures Module-1 Basic Concepts of Data Structures 1.1 System Life Cycle 1.2 Algorithms , Performance Analysis  1.3 Space Complexity, Time Complexity  1.4 Asymptotic Analysis and Notations  1.5 Complexity Calculation of Simple Algorithms Module-2 Arrays and Searching  2.1 Polynomial representation using Arrays  2.2 Sparse matrix  2.3 Stacks  2.4 Queues 2.5 Circular Queues  2.6 Priority Queues 2.7 Double Ended Queues 2.8 Infix to  Postfix Conversion  2.9  Evaluation of Postfix Expression 2.10 Linear Search  2.11 Binary Search Module-3 Linked List and Memory Management 3.1 Linked List -Self Referential Structures  3.2 Dynamic Memory Allocation  3.3 Singly Linked List-Operations on Linked List 3.4 Doubly Linked List 3.5 Circular Linked List  3.6 Stack using Linked List  3.7 Queue
Read more

Stack

Image
A stack is a fundamental data structure in computer science and programming that follows the Last-In, First-Out (LIFO) principle . It is named "stack" because it resembles a stack of items, like a stack of plates or books, where you can only add or remove items from the top. Stacks are used for various purposes in programming and are essential in many algorithms and applications. Let's delve into the details of stacks: Key Operations:  A stack typically supports two primary operations: Push: This operation adds an element to the top of the stack. It is analogous to placing an item on top of the stack. Pop: This operation removes and returns the top element of the stack. It is like taking the top item off the stack. Additionally, stacks often provide the following operations: Peek (or Top): This operation retrieves the top element without removing it. It allows you to examine the top item without modifying the stack. IsEmpty: This operation checks if the stack is empty.
Read more

Quick Sort

Quick sort is a popular sorting algorithm that uses a divide-and-conquer strategy to efficiently sort an array or list. It works by selecting a "pivot" element from the array and partitioning the other elements into two sub-arrays, according to whether they are less than or greater than the pivot. The sub-arrays are then recursively sorted. Here's a detailed algorithm for the Quick Sort algorithm: Algorithm: Quick Sort 1.Choose a pivot element from the array. This can be done in various ways, such as selecting the first element, the last element, or a random element. The choice of the pivot can affect the algorithm's performance. 2,Partition the array into two sub-arrays:     Elements less than the pivot (left sub-array).     Elements greater than the pivot (right sub-array). 3.Recursively apply the Quick Sort algorithm to the left and right sub-arrays. 4.Combine the sorted left sub-array, pivot, and sorted right sub-array to obtain the final sorted ar
Read more